1. Field of the Invention
The present invention relates to a circuit of radio frequency identification (RFID) tag device, particularly to a radio frequency identification (RFID) device implemented with a metal-gate semiconductor fabrication process, which has the advantages of lower fabrication cost, shorter fabrication time, more stable performance, and no extrinsic element needed.
2. Description of the Related Art
Among the Standard CMOS Poly-silicon Logic Processes, the simplest one—the Single-Poly Single-Metal (SPSM) process—still needs to use nine cycles of photomask procedures. Those conventional technologies have advanced to a deep sub-micrometric process or even a nanometric process, and the operational clock of the chip can be promoted thereby. However, the fabrication cost and time thereof is also increased.
At present, RFID tag technology has been widely applied in merchandise bar codes, building security, animal identification, warehousing and distribution management, consumer electronic products, and interactive toys. Refer to FIG. 1 a schematic block diagram of the circuit of a conventional RFID tag 10. A rectification circuit 18 and a resonator 16 comprising an antenna 12 and a capacitor 14 provide electric energy for the RFID tag 10 via a method of electromagnetic induction. Via a logic buffer 20, the resonance frequency of the resonator 16 can be used as the source of the synchronous clock of a RFID tag logic circuit 22. With the synchronous clock, the logic circuit 22 can control a modulator 28 according to a secured identification code stored in a built-in memory 24 or bonding pads 26 to generate a RFID signal.
However, at present, RFID tag is too expensive to be generally used in daily living because the fabrication cost and time of the poly-silicon gate semiconductor process, which the conventional RFID tag adopts, is very high and long. Further, the conventional RFID tag uses a single capacitor or a set of parallel-connected capacitors to store electric charge, which will waste the area of a chip. Furthermore, referring to FIG. 2, the fabrication of the P-type metal oxide semiconductor (PMOS) and the N-type metal oxide semiconductor (NMOS), which are adopted by the conventional RFID tag, need numerous cycles of photomask 30 procedures. Moreover, the fabrication of the conventional RFID tag adopts a sub-micrometric or a deep sub-micrometric or even a nanometric process, which demands higher precision. Therefore, the cost of RFID tag will be the biggest barrier for its competencies.
In the abovementioned problems, the present invention proposes a radio frequency identification device implemented with a metal-gate semiconductor fabrication process to effectively reduce the fabrication cost and time of the RFID device.